Formation of thermal air currents



lDec. 30, 19.41. R. l.. BRANDT 2,268,320

FORMATION OF THERMAL AIR GURRENTS Filed May 5, 1938 2 sheets-sheet 1Dec. 30, 1`941. R. L. BRANDT FORMATION OF THERMAL AIR CURRENTS Filed May5, 1938 2 SheetsfSheet 2 Patented Dec. 30, 1941 UNITED STATES PATENTOFFICE FORMATION F THERMAL AIR CURRENTS Robert L. Brandt, New York, N.Y.

Application May 5, 1938, Serial No. 206,282

4 Claims.

This invention relates to a method and means for the artificialformation of atmospheric thermal currents. More particularly, thisinvention is concerned with the production of atmospheric or thermal aircurrents that are to be utilized in connection with that branch ofaeronautics known as soaring or gliding flight.

The art of soaring or gliding ilight wherein a heavier-than-air machinemaintains itself in flight without the use of a motor and propeller orother mechanical means depends on the pilots finding up-draughts orvertical currents whose velocity is such that while keeping theair-speed of the sail plane above its stalling speed, the ship actuallyrises at a velocity equal to or greater than the speed it wouldnaturally descend because of the gravitational forces acting upon it.

There are several kinds of natural currents or up-draughts that aregenerally found useful for soaring flight. One is a slope current thatis created when a horizontally moving air mass or wind strikes the sidesof a hill or mountain range and is deilected upward. If the velocity ofthe wind is great enough, these currents -or updraughts permit a pilotto gain a higher altitude. Another type of up-draught is the thermal aircurrent that is formed by the heating of the earths surfaces by the sun.

One difficult problem in soaring ight hasv been caused by the fact thatthe pilot must rely solely on mechanical means to get the craft; intothe air usually without the aid of up-draughts, such as a slope current.The greater the altitude initially reached by the craft by mechanicalmeans of launching, the better are the possibilities for the pilotfinding natural up-draughts to aid him in sustaining his night. By meansof an airplane tow, the craft usually is launched at an altitude of frombetween 1,500 and 2,000 feet. By means of a winch tow, under the best ofconditions and with' the best of facilities, the craft will be raisedonly to an altitude of around 1000 feet.

It is therefore an object of the present inven- I tion to artificiallycreate thermal air currents to be used in connection with launching andwith the soaring of the craft, whereby the initial alti-- tude that canbe attained will be greatly above that now possible by purely mechanicalmeans and whereby the pilot can regain altitude naturally lost bygravitational eects.

It is an object of this invention to create these Lip-draughts essentialto guiding Hight by heating large volumes of air either by solar orartificial means.

It is an object of the present invention to create thermal air currentsin the immediate vicinity of the airport so that the craft may bemechanically launched to a relatively low altitude and the pilot maythen spiral upward in the thermal air currents until he has attained thedesired altitude.

The method of and apparatus for attaining the foregoing objects isdescribed in the following specific description and illustrated in theaccompanying drawings wherein:

Fig. 1 is a view of a glider launching field arranged with ground coveraccording to a preferred form of the invention;

Fig. 2 is a detail view showing the ground cover of Fig. l in section;

Fig. 3 is a detail view showing a modified form of ground cover insection;

Fig. 4 is a detail view showing an alternative modification in section;

Fig. 5 is a sectional view showing the dark colored material located ina pit;

Fig. 6 illustrates schematically an arrangement for heating by steam;and

Fig. 7 shows a schematic arrangement for heating by electricity.

The degree of heating of a substance by insolation depends on manyfactors, such as the color, mass, the condition of the surface exposed,the specific heat and thermal conductivity of the substance, and thelocation of the substance on the surface of the earth in relation toother nearby objects. It is a well-known law of physics that surfacecolor plays a very prominent part in the phenomena of radiant heatabsorption and emission. 'I'hus, a black body will under the sameconditions emit a greater amount of sensible heat than a White body perunit surface.

To set up ideal conditions for the formation of thermal currents inaccordance with the invention, it is desirable to have a hot bodysurrounded by a colder body. Under this circumstance, cool air willcontinually flow over the hot area, be raised in temperature, expand,decrease in specific gravity, and therefore rise.

Fig. l illustrates one arrangement for producing thermal air currents. Asubstantially continuous white or light-colored body I3 havingconcentrically disposed thereon a substantially continuous black ordark-colored body II is placed on the surface l2 of the earth forming apart of the airport or glider launching eld. In order that this black ordark-colored heat-absorptive material resting on the layer oflightcolored material I3 may produce up-draughts that are of substantialassistance to the pilot in raising the craft, a considerable surface ofthe earth should be covered by the light-colored body I3 and thedark-colored body II should cover a large part of the center area ofsaid light-colored or non-heat absorptive material as shown in Fig, 1.The amount of h'eat energy obtained per unit area exposed to solarradiation depends on the efficiency of the black body. The surface ofblack body II should be porous in order to aid in a rapid rate of heattransfer between the hot body and the surrounding air. Preferably, themore porous or sponge-like the material of body I I, the moreefficiently will thermal currents be produced thereby as will beexplained later.

A specific example of one type of material that may be used as a heatabsorptive or black body is a composition of petroleum coke (specificheat 2.0) or coal coke intimately bonded with a thick mass of materialof high heat capacity and high thermal conductivity. However, any blackor dark-colored body may be utilized to produce the thermal currents,but those which possess high heat capacity and conductivity and are of aporous nature are preferable.

The portion of the light-colored or white body I3 surrounding the blackbody Il serves as a reflecting surface. This reflecting surface ispreferably white, because a white surface will absorb radiant energyless than any other colored surface, although any other light color maybe used. The area i3, is thus cooler than the A' tends to augment theforce and effect of the thermal currents produced to a greater degreethan thail effected under similar conditions if only the earths surfaceI2 surrounded the black heat absorptive surface II. The White orlightcolored body I3 is placed under the black body II as Well as aroundit to prevent loss of the heat absorbed by the black body from solarsources by absorption by the earth as the case would be if the blackbody rested directly on the earths surface I2. The light-colored orwhite body I3 kbeing between the black body II and the earths surface I2reflects the heat passing through the dark material which wouldotherwise be absorbed by the earth but for the presence of thelight-colored body. However, if conditions or circumstances do notpermit, the black or dark-colored absorptive material may rest directlyon the earth with the white or lightcolored body surrounding the blackbody.

The radiant energy transferred to sensible heat by the black body heatsthe air in contact withthe latter by conduction. On the contrary, theair in contact with the lighter colored surface is not raised to anappreciable extent in temperature because the suns energy is reflectedrather than absorbed by the white surface. 'I'he gases composing theatmosphere, with the exception of water vapor and carbon dioxide, absorbbut little heat. Thus cold air flows over the white surface, makescontact with the warm black body and is raised in temperature, expandsand rises as indicated by the arrows in Fig. 2, to provide a steadyvertical draught (thermal) of air.

The white body may be composed of any white or off-white color.v Itshould preferably be a thermal insulator as well. PracticalconsiderationsV are that the material should be water insoluble so thatit will remain in place during wet seasons. For example, water insolublesalts like chalk, crystallized gypsum,v magnesium oxide, etc. may beemployed as the white body. Water films also are useful and may be soused, as for example a small island that is covered with a black body,the water surrounding the island being of sufficient depth to effect thenecessary temperature difference.

Where conditions are such that it would be impracticable to employ thelayer of light-colored material described above, adequate results can beobtained by eliminating the such material and allowing the dark-coloredbody to rest directly on the earths surface. Being more absorptive thanthe earth, the black body will emit more sensible heat than the earthssurface surrounding it, hence there will be a flow of air from the areaabove the bare earth across to the area above the dark-colored surface.There said air will be heated to cause the production of rising thermalair currents. Fig. 3 shows this form.

Another improvement is illustrated in Fig. 4. The black body II ordark-colored absorptive surface is supported above the surface I2 of theground. It is well known that the rate of heat. transfer between a solidand a gas, inthis case the heat sponge II and the air in contact withit, respectively, is among other things a function of the velocity ofthe gas. In this embodiment, the optimum condition for producing thermalair currents is realized by utilizing a thin layer of porous blackmaterial II intimately bonded to a porous mass of material of high heatconductivity such as iron shavings or brass turnings.

The interstices should be large to permit flow of air throughout themass with lowpressure drop. Instead of the black body or large massmerely contacting a relatively stagnant film of air, its elevatedposition permits theV free vcirculation of the air through it with theresultant creation of a much more powerful up-draught. In this casealso. the efficiency is increased by surrounding the sponge orabsorptive body I I by the lightcolored reflecting surface I3 whichrests on the earths surface and extends under the black body as shown inFig. 4.

The black porous body II may also be located in a pit Il with the wallsand bottom I5 of the pit Il so arranged that they reflect the radiantsolar rays onto the surface of the body II. Such an arrangement willminimize the effect of natural winds and thereby permit a betterdirectional control of the thermal air currents as they are intheprocess of artificial formation. The walls and bottom-of the pit arepreferably white in color. 'I'he black body in this case is raised abovethe bottom of the pit wlth'space left bei tween the outer edge of theblack body and the walls of the pit so that the air currents may freelycirculate around and under the dark-colored or black body. Fig. 5 showsthis variation.

The heat absorptive material II or black or dark-colored porous body maybe artificially heated and so produce substantially the same results asthose effected when the energy derived from the suns rays is utilized toproduce rising thermal air currents or up-draughts. The heat absorptionmaterial may be artificially heated by means of steam and/or waste fluegases, either directly or indirectly. Direct heating, for example withsteam, offers the advantages of i 1) reducing the density of the airbecause ci the lower molecular weight of water relative to that of air;(2) obtaining better heat exchange; (3) giving greater heat absorptionbecause the water vapor is one of the few gases normally occurring inair that will absorb heat from the sun by direct radiation.

Hence, as shown in Fig. 6, steam pipes I6 may be embedded in a porous orheat retentive sheet I 1 covering the-surface of the earth in thevicinity of the airport. The heat absorptive material I1 is thus heatedby the steam in the pipes I., and as the area over this surface I1 iswarmer than that over the surface of the earth surrounding it, thethermal air currents are produced on the same principle as that involvedin the case of solar heating of the black or disk-colored body I l ofhigh absorptive capacity.

As shown in Fig. 7, absorptive or porous sheet I8 may be heated by anysuitable electrical arrangement such as encased resistors I9, and rising thermal currents produced from heat effected thereby.

From the foregoing it will be observed that a thermal current may beformed in the immediate vicinity of the airport so that getting into theair at suillcient altitude is no problem. All that is necessary is to bewinch or auto-towed to a relatively low altitude into the thermalcurrent. At this point the pilot releases the tow rope and may thenspiral upward in the thermal current to gain the required altitude.Ideally the location of the black body would be in a small valley. Awind blowing the heated air against the sides of the surrounding hillswould give the effect of both thermal and up-draught and this is ofgreat advantage to the soaring pilot.

I claim:

1. In combination, a field for the launching of gliders, said fieldhaving a predetermined area, a layer of porous heat retentive materialcovering a portion of said field, pipes horizontally incorporated withsaid material, and means for passing steam through said pipes to heatsaid heat retentive material and cause rising thermal air currents to beproduced.

2. In a glider launching field, means for the artificial production ofrising thermal air currents comprising a circular layer of absorptivematerial covering an area of the earths surface of at least three acres.and means for heating said material.

3. An arrangement for producing rising or vertical thermal air currentsthat comprises a substantially continuous and circular dark-coloredheat-absorptive surface surrounded by and resting on a light-coloredsurface, said light-colored surface disposed over the surface of theearth and covering an area of at least several acres. the saiddark-colored surface absorbing radiant energy from the sun's rays whilethe lightcolored surface largely reflects said energy. thereby creatinga now of the cooler -air over the light-colored surface to the warmerdark-colored surface. where said cooler air is heated, expands, and

then rises. Y

4. An arrangement for producing rising thermal air currents thatcomprises a circular layer. of dark-colred porous 4heat-absorptivematerial exposed to the action of the suns rays, surrounded by andresting on a circular layer of light-colored material, saidlight-colored material being disposed over the surface of the earth andcovering an area of the earths surface of at least several acres, theporous material absorbing the heat from the suns rays more efficientlythan the light-colored material, whereby a flow of the air is effectedover the light-colored material toward the area over the porous materialwhere the air becomes heated, expands, and rises.

ROBERT L. BRANDT.

